FIG. 1 illustrates an ionization detector. One such detector is that described in U.S. Pat. No. 4,129,783, to Housten, et al., which is hereby incorporated by reference. As shown in FIG. 2, radiation 3 is collimated by a collimating slit 6 and enters an ionizing chamber 9 contained in a housing 10. (The collimating slit is not shown in FIG. 1.) The chamber 9 contains an ionizable medium such as Xenon gas at a pressure of, for example, 1000 psi. A steel gasket 12 assists in sealing the two parts 15 and 18 of the housing 10. Parts 15 and 18 are held together by bolts (not shown). A substrate 19 enters the chamber 9 through a slot 20 (in FIG. 1) containing a seal 28. The substrate supports a plurality of conductors 24.
When the radiation 3 ionizes the medium, such as at point 21 in FIG. 2, an electron becomes separated from a Xenon atom, and the electron is captured by one of the conductors 24 in FIG. 1, thereby depositing a charge on the conductor. The spatial charge distribution on the conductors is thus a function of the spatial intensity distribution of the incoming radiation 3, and thus can be used to infer the material density distribution of an object through which the radiation passes en route to the ionization chamber 9. Thus, the substrate-conductor system can be considered as a sensor. Viewed another way, the conductors 24 in FIG. 1 serve a function analogous to X-ray film.
An unexpected phenomenon has been found in the seal 28 which seals the substrate 19 in FIGS. 1 and 2 to the housing 10. For example, when the chamber 9 is inflated to 1000 psi, the housing part 18 tends to deform or bow into the position shown (in grossly exaggerated form) by dashed line 30 in FIG. 2, as well as perhaps to deform in other, more complicated ways. Further, repeated pressurization and depressurization causes cyclic loading upon the seal 28 which is believed to also cause seal deformation. Some such seals 28 have been found by Applicant to fail, perhaps from deformation.